Resolving Azimuth Ambiguity Using Vertical Nature of Solar Quiet-Sun Magnetic Fields

TL;DR

This paper introduces a fast, non-iterative method for resolving the 180-degree azimuth ambiguity in solar magnetic field measurements, based on the assumption of predominantly vertical magnetic fields in certain solar regions.

Contribution

The proposed method leverages the vertical nature of solar magnetic fields to disambiguate azimuth angles efficiently, serving as a quick initial step for more complex algorithms.

Findings

Successfully disambiguates 60-85% of pixels in full-disk magnetograms.

Non-iterative and insensitive to noisy pixels.

Applicable to regions with predominantly vertical magnetic fields.

Abstract

The measurement of solar magnetic fields using the Zeeman effect diagnostics has a fundamental 180 degree ambiguity in the determination of the azimuth angle of the transverse field component. There are several methods that are used in the community and each one has its merits and demerits. Here we present a disambiguation idea that is based on the assumption that most of the magnetic field on the sun is predominantly vertical. While the method is not applicable to penumbra or other features harboring predominantly horizontal fields like the sheared neutral lines, it is useful for regions where fields are predominantly vertical like network and plage areas. The method is tested with the full-disk solar vector magnetograms observed by the VSM/SOLIS instrument. We find that statistically about 60-85 % of the pixels in a typical full-disk magnetogram has field inclination in the range of 0-30 degrees with respect to the local solar normal, and thus can be successfully disambiguated by the proposed method. Due to its non-iterative nature, the present method is extremely fast and therefore can be used as a good initial guess for iterative schemes like nonpotential field computation (NPFC) method. Furthermore, the method is insensitive to noisy pixels as it does not depend upon the neighboring pixels or derivatives.